#!/bin/python3

import sys

def sumOfGroup(k):
        first = (k*(k-1))+1;
        sum=0;
        i=0
        while(i<k):
            sum+=first;
            first+=2;
            i+=1;
        return sum;

if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)